What is the minimum amount of DCA to make the fees of Endowus worth it. Open to suggestions on other platforms as well?

1. For robos, no need to care how much you DCA. There's no transaction fee. There's only access/management/platform fees.

2. If you need the money in your CPF in the short-term to buy house, best is to just leave it. Use your cash to invest for the long-term. As for lump sum vs DCA, in a downtrend market, it's better to DCA and in an uptrend, lump sum. But I wouldn't know how the market is going to behave so can just aim to stay invested for a longer time (lump sum) and increase the "time in market".

3. I've never received dividends from Endowus. It's probably reinvested. You will need to redeem your investments and do a manual housing refund on the CPF website to "pay any accrued int for HDB purchase".

1) what is the min amount i should DCA monthly to make the fee % lowest?

Endowus and other robos I know charge based on AUM, so there is no "minimum to make the fees lowest", unlike traditional brokers.

3) does the dividends i earn help pay any accrued int for HDB purchase?

If you mean whether accured interests will decrease when dividends are credited, no.

accured interests will continue to be reflected as accured interests unless there is a capital repayment (meaning cash repayment, or after sales proceeds go back to CPF)